<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div>
        <!-- 当条件为 true 时执行的代码  -->
        <p>如果时间早于 20:00,会获得问候 "Good day"。</p>
        <button onclick="myFunction()">点击这里</button>
        <p id="demo"></p>
        <script>
            function myFunction() {
                var x = "";
                var time = new Date().getHours();
                if (time < 20) {
                    x = "Good day";
                }
                document.getElementById("demo").innerHTML = x;
            }
        </script>
    </div>
    <hr />
    <div>
        <p>点击这个按钮，获得基于时间的问候。</p>
        <button onclick="hbttnbtn()">点击这里</button>
        <p id="aaaa"></p>
        <script>
            function hbttnbtn() {
                var x = "";
                var time = new Date().getHours();
                if (time < 20) {
                    x = "Good day";
                }
                else {
                    x = "Good evening";
                }
                document.getElementById("aaaa").innerHTML = x;
            }
        </script>
    </div>
</body>

</html>